Comparative Pathology Shared Resource Summary The mission of the Comparative Pathology Shared Resource (CPSR) is to provide comprehensive pathology support for Masonic Cancer Center (MCC) members who use laboratory animals in their research. The CPSR is a critical resource for projects using animal tissues and is essential for publications involving pathological changes in tissues. The CPSR operation has been led by M. Gerard O'Sullivan, MVB, PhD, since 2009 and is supported by Technical Coordinator Katalin Kovacs, PhD; histotechnologist Paula Overn, HT, QIHC; and postdoctoral research pathologist, Flaviu Tabaran DVM, PhD. Dr. O'Sullivan has more than 25 years of experience in comparative and experimental veterinary pathology. The laboratory prepares appropriately processed fixed or frozen tissues for histology and immunohistochemistry (IHC). Particular strengths of the laboratory are in doing non-routine, challenging, or tedious histological preparations; performing IHC preparations on multiple markers; developing new IHC protocols for markers of interest; and performing IHC on bone. Board-certified veterinary pathologists provide expert gross and histopathologic analysis, generate high- resolution digital images of specimens, and provide intellectual input on study design and manuscript preparation for research projects and grant applications. The CPSR also has considerable experience in developing new protocols and techniques and has developed 121 new IHC markers since 2012. In addition, the CSPR has developed double-labeling techniques to simultaneously detect several combinations of proteins. Requests for quantification of marker expression and histomorphometric evaluations have increased, and CSPR has developed expertise to accommodate these requests. Weekly staff meetings and annual feedback from CPSR users ensure that the resource is able to meet the needs of MCC members.